As mobile devices are technically developed and in increasing demand, the demand for secondary batteries as an energy source rapidly increases. Although nickel cadmium batteries or hydrogen ion batteries have been used as secondary batteries according to the related art, lithium secondary batteries, which are freely charged and discharged due to almost no memory effect as compared with nickel-based batteries and have extremely low self-discharge rate and high energy density, are widely used in recent years.
Such lithium secondary batteries mainly include a lithium-based oxide and a carbon material as a positive electrode active material and a negative electrode active material, respectively. Lithium secondary batteries include an electrode assembly, in which a positive electrode plate and a negative electrode plate respectively coated with a positive electrode active material and an negative electrode active material are arranged with a separator therebetween, and an exterior, that is, a battery case, in which the electrode assembly and an electrolyte are sealed and received.
Lithium secondary batteries include a positive electrode, a negative electrode, a separator interposed therebetween, and an electrolyte, and are classified into lithium ion batteries (LIBs), polymer lithium ion batteries (PLIBs), and the like, depending upon what are respectively used as a positive electrode active material and a negative electrode active material. Generally, a positive or negative electrode active material is coated on a current collector of aluminum or copper sheet, mesh, film, foil, or the like, and then dried, thereby forming electrodes of lithium secondary batteries.
In such secondary batteries, a battery cell is protected by using at least one of a cover, a case, and an end plate. That is, a battery cell is received in a cover, case, or end plate, thereby protecting the battery cell. In the case of secondary batteries according to the related art, a cover, a case, or an end plate is coupled by using various fastening members, for example, a long bolt or the like. However, to perform fastening by way of a fastening member such as a long bolt or the like, a fastening portion for a long, bolt needs to be formed in a cover, a case, or an end plate, and there are problems in that an overall size of a secondary battery is increased due to such a fastening portion for a long bolt, and that working time is increased due to a process for fastening a long bolt.